1. Field of the Invention
The invention herein relates to the assessment of human ocular coordination for the diagnosis of phorias for treatment of dysfunctional phorias.
2. Background of the Prior Art
Eye care professionals, such as ophthalmologists and optometrists, routinely examine patients to assess the ocular coordination of the patient's eyes. Most people possess the ability innately to bring into satisfactory alignment the individual binocular vision images registered by each of the person's eyes. However, a substantial number of individuals are afflicted with various physical conditions which limit or prevent proper binocular vision. A principal class of such conditions, particularly those which pertain to horizontal coordination of images, are phorias. These types of visual conditions have long been described in the literature; see, for instance, Newell, Ophthalmology: Principles and Concepts (6th ed.; 1986), Chapter 21 and Michaels, Visual Optics and Refraction: A Clinical Approach (3rd ed.; 1985), Chapter 18. While some phorias, such as orthophoria or exophoria, are either considered good or at least not normally a significant dysfunction, others, such as esophoria, are considered to constitute cosmetic and/or functional dysfunctions. Among the effects and elements involved in such dysfunctional conditions are poor or non-existent depth perception, unequal muscle balance, dominance of one eye's image over that of the other eye, and inability to make independent vertical or horizontal coordination of images.
There have in the past been devices designed to enable an eye care professional to attempt to assess a patient's ocular coordination. Several types of devices commonly referred to as phorometers were designed and used; some of these are referred to in the aforesaid Michaels text, Chapter 18, and others are briefly described in Schapero et al., Dictionary of Visual Science (2nd ed.; 1968), pp. 327 and 540. A few of these devices have also incorporated means for obtaining a quantitative value for the degree of non-coordination exhibited by a patient. These, however, have been uniformly cumbersome and difficult to use for the ordinary practitioner. Consequently, while a few such devices still exist, they are for the most part found only in teaching facilities where they are operated by professors or other highly trained experts for the purpose of providing professional students with an understanding of ocular coordination conditions and abnormalities. Most such devices are very old, and they are essentially not practical for use by the regular eye care professional in routine patient assessment.
Consequently, virtually all current ocular coordination assessment by eye care professionals is done on a subjective basis. The patient is shown a succession of preformed images whose correct appearance is known to the examiner. The patient is then asked to state verbally what he or she sees while viewing the image. From the patient's verbal description, the examiner can make a subjective assessment as to whether the patient is seeing the image correctly or to what degree the patient's view of the image appears to differ from the correct appearance of the image. Needless to say, this type of assessment suffers from a number of deficiencies.
1. Most importantly, the examiner's assessment is wholly dependent upon the ability of the patient to express his or her view of the image verbally and in complete and appropriate detail. Thus the examination is severely limited when the patient is inarticulate or unable to express his or her thoughts accurately (such as where the patient is a foreign language speaking person not fluent in the examiner's language). Of course, the method fails completely where the patient is unable to express a coherent description of what he or she sees, as is the case in attempting to examine infants, small children or the developmentally immature.
2. Even where the patient is able to provide a reasonably comprehensive verbal description of the image he or she sees, establishment of a standard diagnosis is still very difficult or impossible, since even articulate speakers will describe the same image in different ways. This makes it very difficult for the examiner to confirm whether or not a particular patient's condition is equivalent to other predetermined levels of coordination, since the patient, while assumably seeing the same visual image, will normally not describe it in precisely the same terms as the standard definition.
3. If as is common, the eye care professional reshows the various images several times over the course of an examination, different apparent results may occur since the patient may not necessarily describe the image in identical terms each time it is repeated.
4. Even where the patient provides a good description of what he or she sees, the examiner's ability to assess that description for proper prescription of corrective lenses will still be quite subjective and only marginally quantitative. Since the patient's description of the view each time it is presented is not directly reproducible, the examiner can only get a general idea of what degree of correction is required for prescriptive lenses. The examiner must therefore, by trial and error, present to the patient a series of various corrective lenses until the patient's description of the image viewed with a particular set of corrective lenses appears to the examiner to correspond to what the examiner knows is the correct description of the image. Of course, since the final prescription is still dependent upon the examiner's subjective evaluation of the particular verbal description that the patient has articulated, which itself was subjective, the prescription may or may not in fact be optimum for that patient.
It would therefore be of great advantage to the eye care field to have available a simple and accurate objective method of providing a precise and reproducible quantitative assessment of a patient's ocular coordination. Such a device would advantageously be of equal and accurate use by eye care professionals for all types of patients, regardless of their ability to verbally express the nature of the image viewed. It would also be relatively inexpensive and of simple enough design that it could be used in medical, educational or psychological practice, not only directly by the professional but also by technical assistants having only a relatively limited degree of training. Further, such device should provide a clear and precise quantitative measurement which allows the eye care professional to unequivocally prescribe the appropriate corrective lenses for the particular patient's condition. Finally, it should be equally usable with adults and children.